how to array with 2 group objects
Unfortunately groups (even instanced) can not have an array modifier.

Your best bet will be to add the array to one object, then select the other, shift select the object with the array and press Ctrl + C and select Copy Modifiers.

Make sure you use Constant Offset or Object Offset and not Relative Offset.





By request, I will add an explanation how to create the target for the array with circular symmetry


Snap an empty to the object, which has the array modifier: arrayTarget
Snap an empty to the center of the circle: circlePivot
Set the object Array Offset to: arrayTarget
Parent arrayTarget to circlePivot
Rotate the circlePivot the desired amount.